* Astronomy

Title: A Photometric Redshift of z ~ 9.4 for GRB 090429B
Authors: A. Cucchiara, A. J. Levan, D. B. Fox, N. R. Tanvir, T. N. Ukwatta, E. Berger, T. Krühler, A. Küpcü Yolda, X. F. Wu, K. Toma1, J. Greiner, F. Olivares E., A. Rowlinson, L. Amati, T. Sakamoto, K. Roth, A. Stephens, J.P.U. Fynbo, J. Hjorth, D. Malesani, P. Jakobsson, K. Wiersema, P. T. O'Brien, A. M. Soderberg, R. J. Foley, A. S. Fruchter, J. Rhoads, R. E. Rutledge, B. P. Schmidt, M. A. Dopita, P. Podsiadlowski, R. Willingale, C. Wolf, S. R. Kulkarni, P. D'Avanzo

Gamma-ray bursts (GRBs) serve as powerful probes of the early Universe, with their luminous afterglows revealing the locations and physical properties of star forming galaxies at the highest redshifts, and potentially locating first generation (Population III) stars. Since GRB afterglows have intrinsically very simple spectra, they allow robust redshifts from low signal to noise spectroscopy, or photometry. Here we present a photometric redshift of z ~ 9.4 for the Swift detected GRB 090429B based on deep observations with Gemini-North, the Very Large Telescope, and the GRB Optical and Near-infrared Detector. Assuming an Small Magellanic Cloud dust law (which has been found in a majority of GRB sight-lines), the 90% likelihood range for the redshift is 9.06<z<9.52, although there is a low-probability tail to somewhat lower redshifts. Adopting Milky Way or Large Magellanic Cloud dust laws leads to very similar conclusions, while a Maiolino law does allow somewhat lower redshift solutions, but in all cases the most likely redshift is found to be z>7. The non-detection of the host galaxy to deep limits (Y(AB) ~ 28, which would correspond roughly to 0.001L^* at z=1) in our late time optical and infrared observations with the Hubble Space Telescope, strongly supports the extreme redshift origin of \grb, since we would expect to have detected any low-z galaxy, even if it were highly dusty. Finally, the energetics of GRB 090429B are comparable to those of other GRBs, and suggest that its progenitor is not greatly different to those of lower redshift bursts.

Read more  (4641kb, PDF)

BETTING ON THE MOST DISTANT GAMMA RAY BURST EVER SEEN: EXTREME DISTANCE DETERMINED WITH GEMINI OBSERVATORY IMAGES

Gemini Observatory colour composite image of the afterglow of GRB 090429B - a candidate for the most distant object in the universe. This "izH" image has been constructed from three images taken at the Gemini Observatory North telescope through different optical and infrared filters (the infrared images were obtained using the Gemini Near-Infrared Imager, NIRI, optical, non-detection data from the Gemini Multi-Object Spectrograph, GMOS). The red colour results from the absence of all optical light, which has been absorbed by hydrogen gas in the distant universe. Without that absorption, the afterglow colour would be bluer than any of the galaxies and stars seen in this field of view. The position of the afterglow is indicated.


A unique set of images from the Gemini North telescope in Hawaii clearly reveals the infrared afterglow of this powerful burst. More importantly, the data allowed the researchers to estimate its distance with a relatively high degree of certainty, placing it near the edge of the observable universe.
The finding, announced today at the American Astronomical Society meeting in Boston Massachusetts, follows the evolution of a gamma ray burst (GRB 090429B) discovered by NASA's Swift satellite in April of 2009. GRBs like this one are a consequence of the deaths of massive stars, with an initial brief burst of high-energy emission gradually fading to an afterglow of light at other wavelengths. The subsequent afterglow was detected only at infrared wavelengths using the Gemini North telescope.

Read more